Hoisting grab

ABSTRACT

A hoisting grab of which the grab housing, provided with a hoisting eye, comprises at least two spaced webs between which one gripping cam is pivotally mounted, the webs having aligned recesses situated in the path of said gripping cam, adapted to receive an edge portion of an article to be hoisted, wherein the webs are each composed of two or more separate layers of sheet metal.

United States Patent Stijger 51 July 11, 1972 [54] HOISTING GRAB [72] Inventor: Adrianus G. Stijger, Haarlem, Netherlands [73] Assignee: Interlas N.V., Soesterberg, Amersfoortses- 'traat, Netherlands [22] Filed: Feb. 17, 1971 21 App1.No.: 116,100

s21 U.S.Cl .f. ..294/104 51 1111.01. ..B66cl/48 5s FieldofSearch ..294/l04,106

[56] References Cited UNITED STATES PATENTS 2,654,631 10/1953 Renfroe ..294/104 2,430,544 11/1947 Walker ..8 l/3.8

Primary Examiner-Even C. Blunk Assistant Examiner-Johnny D. Cherry Att0rney-Marshall & Yeasting [57] ABSTRACT A hoisting grab of which the grab housing, provided with a hoisting eye, comprises at least two spaced webs between which one gripping cam is pivotally mounted, the webs having aligned recesses situated in the path of said gripping cam. adapted to receive an edge portion of an article to be hoisted. wherein the webs are each composed of two or more separate layers of sheet metal.

1 Claim, 1 Drawing Figure norsrmc GRAB BACKGROUND OF THE INVENTION The invention relates to hoisting grabs of the type in which the grab housing, provided with a hoisting eye, comprises at least two spaced webs between which one gripping cam is ivotally mounted and in which the webs have a recess intersecting the path of said gripping cam and adapted to receive an edge portion of an article to be hoisted.

Hoisting grabs of this type are known in many forms and are widely applied, as for hoisting and handling plates and profiles in rolling mills, in ship yards, in machine shops and similar places. The webs of the grab housings thereof are manufactured from a relatively thick plate steel or are obtained as forgings. In the first mentioned case the webs are fixed relative to each other either by welding or by means of bolts with the intermediary of spacer elements, whereas in the second case mostly integrally forged spacing ridges are used. The recess adapted for receiving an edge portion of an article to be hoisted is usually formed by a slot shaped edge recess as a result of which the webs are generally U-shaped. The gripping cam may be pivoted from the space between the U-legs situated at one side of the webs to a position in the slot in order to clamp an article received in said slot against the opposed U- legs of the webs, for which purpose a fixed jaw has been provided at the slot side corresponding with said opposed U-legs. Pivoting the gripping cam into the operative clamping position takes place under the influence of the hoisting eye which is movably guided with regard to the grab housing, said eye being connected to the gripping cam either directly or with the intermediary of a link. In order that the articles to be hoisted may be picked up even from relatively narrow spaces such as from a series of articles disposed closely together, a slender construction of the grab is of great importance. This implies that the width of the U-legs of the webs of the grab housing should be kept as small as possible. On the other hand the grab, which in practice is dimensioned for hoisting loads of one to several tens of tons, must have the required fivefold safety as regards its strength. In practice the weakest and therefore the critical point of the grab now appears to be formed by the transitions between the bridge portions and the leg portions of the U-shaped webs and particularly by the transitions disposed opposite the pivotally mounted gripping cam. Tests have shown that cracking tends to take place at the last mentioned transition points. It is clear that the tendency to cracking is greater when the webs and especially their U-legs are more slender. In order to obtain nevertheless the required strength the thickness of the webs is made correspondingly greater.

SUMMARY OF THE INVENTION The invention now provides a hoisting grab of the above mentioned general type which is distinguished from the wellknown hoisting grab constructions in that its webs are each composed of two or more separate layers of sheet metal. Experiments have shown that based on a predetermined overall wall thickness laminated web construction according to the invention provides a much greater safety against cracking than a hoisting grab having integrally formed webs. In particular it has been found that with a given load, which leads to cracking in the webs of a known hoisting grab, the hoisting grab according to the invention only shows a small outward bending of the U-legs without the grab thereby becoming unsafe and therefore unserviceable. This outward bending without cracking appears to have been permitted by the fact that the individual layers of the relative U-legs have been wrinkled slightly at the web periphery when seen from the side. This means in fact that the compression stresses arising in the outer region of the critical U-legs when loading to the required safety limit, are greater than the strength of the separate layers of the U-legs of the grab according to the invention, whereas said compression stresses in the known grab construction remain below a value corresponding to the strength of the complete U-legs.

Therefore the hoisting grab according to the invention provides, with a given dimensioning for a given maximum operating load, a considerably greater safety or in other words for a given maximum operating load and a given safety it may be dimensioned essentially lighter.

The laminated web construction in the grab according to the invention further permits the application of cheaper manufacturing techniques when providing the slots and other recesses which have to be made in the webs. Particularly the laminated construction according to the invention permits the slots and holes to be obtained by punching rather than by milling and drilling, with the additional effect of such punching being connected with cold deformation and the inherent strengthening of the edges of the slots and bores, which enhances the resistance to wear.

BRIEF DESCRIPTION OF THE DRAWING The drawing is a perspective view of a hoisting grab embodying the invention, with a portion broken away to show the internal construction.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hoisting grab shown in perspective in the drawing is of a type which is particularly adapted for hoisting plates and similar articles in a vertical position. The housing of said grab comprises two webs l and 2, which are substantially identical in shape, and which by means of three spacer elements 3 are kept spaced parallel from each other. The spacer elements 3 may be bolts with corresponding nuts and spacer sleeves provided between the webs around the bolt shanks. The webs l and 2 each have a notch or edge recess 4 for receiving an edge portion of a plate or similar article to be hoisted. At the side away from the recess 4 a hoisting eye 5 has been provided, the shaft 50 of which extends into the space between the two webs l and 2, whereas the eye 5b itself takes a completely free position in order to permit it to be engaged for instance by a hook or similar hoisting means. The hoisting eye shaft 5a is at its end remote from the eye 5!; connected pivotally around a pin 6 with two links 7 which at their other ends are pivotally mounted around a pin 8 connected to a gripping cam 9. The cam 9 is pivotally mounted around a pin 10 between the depending legs la and 2a of the webs l and 2, which due to the slot shaped recess 4 are generally U-shaped. The serrated portion of the cam 9 cooperates with a fixed jaw 11 which has been provided as a bridge piece within the slot 4 between the web legs 1b and 2b.

The ends (not shown in the drawing) of the pivot pin 6 which extends laterally beyond the links 7 are slidably guided in slots provided at the inner sides of the webs, such that the pin 6 with the hoisting eye 5 is movable in the direction of the arrow.

In operation the hoisting eye 5 is moved outwardly from the space between the webs l and 2 under the influence of the pulling force applied to it. This movement is transformed by the links 7 into a rotational clockwise movement of the cam 9 around the pin 10. Thereby the serrated cam portion 9a is moved towards the fixed jaw 1 l for clamping a plate which has been inserted with its edge portion into the slot shaped edge recess 4. Said movement, however, is only possible after a locking cam 13, which is fixed upon a pivotally mounted pin 12 in the space between the webs 1 and 2, has been placed by means of the operating lever 14 in the inoperative position shown in the drawing. In the drawing the cam 9 and therefore also the links 7 and the hoisting eye 5 have been shown in an intermediate position. One of the end positions corresponds to that in which the pivot pin 6 is aligned with the opening 15 in the web 1, said opening serving to enable the mounting of the pivot pin when assembling the grab. In said end position the locking cam 13 may be turned counter-clockwise to its locking position by means of the lever 14, in which position the cam engages with its nose 13a the portion 7a of at least one of the links 7. The hoisting grab is then locked with the cam 9 in the retracted and therefore inoperative positionv Between the locking cam 13 and the link 7 cooperating therewith a tension spring has been mounted under pre-tension which for the sake of simplicity is indicated by a dot-dashline 16.

So far the grab is generally of known construction. However, the construction of the two webs l and 2 is completely novel. These webs each consist of a group of separate layers of sheet metal, which layers are substantially identical in shape, and are indicated as 1', l, 1 and 2', 2, 2" respectively. The advantage of this web construction is more clearly illustrated by the drawing, which shows for the web 1 by means of broken lines how the separate layers 1, l", 1" of said web will buckle when the grab is overloaded, rather than breaking along the breaking line X as is the case with the grab constructions known heretofore. in order that each sheet metal layer may buckle when overloaded as indicated in broken lines, instead of breaking along the line X, it is necessary that the resistance to failure under tension of the sheet metal at the points of greatest stress on the inner edges of the legs 1b be greater than the resistance to failure under compression at the points of greatest stress on the outer edges of the legs 1b, so

that each layer of sheet metal in the legs 1b buckles at its outer edge before it tears at its inner edge.

In the embodiment shown each of the webs consists of four layers. However, it will be clear, that also a greater number of layers may be chosen while under same circumstances also the application of two layers may meet the purpose in view.

l claim:

1. A hoisting grab comprising two spaced webs which are substantially identical in shape and each of which has two depending legs, a gripping cam pivotally mounted between the first leg of one web and, the corresponding first leg of the other web for clamping the work against the second legs, wherein each web is composed of at least two layers of sheet metal which are substantially identical in shape. the resistance to failure under tension of the sheet metal at the points of greatest stress on the inner edges of the second legs being greater than the resistance to failure under compression at the points of greatest stress on the outer edges of the second legs under extreme pressure applied by the cam, so that each layer in the second legs buckles at its outer edge before it tears at its inner edge. 

1. A hoisting grab comprising two spaced webs which are substantially identical in shape and each of which has two depending legs, a gripping cam pivotally mounted between the first leg of one web and, the corresponding first leg of the other web for clamping the work against the second legs, wherein each web is composed of at least two layers of sheet metal which are substantially identical in shape, the resistance to failure under tension of the sheet metal at the points of greatest stress on the inner edges of the second legs being greater than the resistance to failure under compression at the points of greatest stress on the outer edges of the second legs under extreme pressure applied by the cam, so that each layer in the second legs buckles at its outer edge before it tears at its inner edge. 